linux-kernel - Re: git pull on linux-next makes my system crawl to its knees and beg for mercy

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Date:	Wed, 23 Dec 2009 16:27:20 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	"Luis R. Rodriguez" <mcgrof@...il.com>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-kernel@...r.kernel.org, Bob Copeland <me@...copeland.com>
Subject: Re: git pull on linux-next makes my system crawl to its knees and beg 
	for mercy

On Fri, Dec 18, 2009 at 11:03 PM, Luis R. Rodriguez <mcgrof@...il.com> wrote:
> On Fri, Dec 18, 2009 at 1:56 PM, Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>> Hi Luis,
>>
>> On Fri, 18 Dec 2009 09:26:29 -0800 "Luis R. Rodriguez" <mcgrof@...il.com> wrote:
>>>
>>> I tend to always be on a 2.6.32 kernel + John's queued up patches for
>>> wireless for the next kernel release (I use wireless-testing). My
>>> system is a Thinkpad T61, userspace is Ubuntu 9.10 based (ships with
>>> git 1.6.3.3) and I kept an ext3 filesystem to be able to go back in
>>> time to 2.6.27 at will without issues.  I git clone'd linux-next a few
>>> weeks ago. After a few days I then tried to git pull and my system
>>> became completely unusable, It took *ages* to open up a terminal and
>>
>> The start of the daily linux-next boilerplate says:
>>
>>> If you are tracking the linux-next tree using git, you should not use
>>> "git pull" to do so as that will try to merge the new linux-next release
>>> with the old one.  You should use "git fetch" as mentioned in the FAQ on
>>> the wiki (see below).
>>
>> (Unfortunately, the wiki seems to be unavailable at the moment)
>>
>> I am guessing that the merge that git is attempting is killing your
>> laptop (though besides the number of common commits I am not sure why).
>> Please try using "get fetch" instead.
>
> Indeed, I learned my lesson now. Thanks for the details.
>
> Now granted, even if 'git merge' is killing my laptop due to the
> conflicts of the insane merge I was trying to do it *still* should not
> make my box completely unresponsive for so long. And given that I'm
> using mostly distribution specific kernel config options and my have
> ruled out my hard drive it seems a general serious kernel issue even
> down to 2.6.27. Whatever git is doing I'm sure other userspace
> software can also end up generating and would make any user go
> completely bananas. I was about to rip my hair out.

Git gurus would know it by heart, but I am not one. So if I were you,
I would just do a generic diagnostic run. What is it git is doing
so that machine slows down that much? Is it spawning a lot
of running processes? Is it allocating/using so much memory
that your box goes into a severe swap storm?

I guess it is the latter. If it is, then it's not a kernel problem -
kernel can't magically make your system adequately handle a workload
which needs 3 GB for working set when the box only has 2 GB of RAM.
It _will_ be very slow.

--
vda
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